1. Technical Field
The present disclosure relates to a UV-resistant gelatin/silica viral particle, preparation method and uses thereof.
2. Description of Related Art
Traditionally pest control has been dominated by the use of chemical insecticides. Although they are fast acting, these chemicals are sometimes environmentally unattractive. In addition, many chemicals used in insect pest control are not species-specific and may affect non-target animals as well as the target pest. Furthermore, these chemicals or their by-products can sometimes persist in the environment for long periods of time.
Biological control, the use of living organisms to control insect pests, has become increasingly more acceptable as a means for controlling pests successfully. For example, the bio-insecticide Bacillus thuringiensis (Bt), is used for control of spruce budworm (see U.S. Pat. No. 5,061,489). However, some recent concerns over the specificity of Bt have resulted in the recommendation that it not be used in areas where there are endangered Lepidoptera. Ecological interests have resulted in a shift in emphasis to examine and develop other microbial products, including the insect viruses.
Insect viruses, such as Baculoviruses, are naturally occurring insect pathogens that are considered to be host specific and environmentally safe. They can persist for years to impact on several generations of insects. Baculoviruses are a large group of insect viruses that are known to infect over 500 different insect species, mainly Lepidoptera. Some baculoviruses infect insects which are pests of commercially important agricultural and forestry crops. Such baculoviruses are potentially valuable as biological control agents. There are sixteen countries using baculoviruses to control Lepidoptera and more than 30 species of baculoviruses have been developed as microbial insecticides.
Baculovirus subgroups include nuclear polyhedrosis viruses, now called nucleopolyhedroviruses (NPVs) and granulosis viruses, now called granuloviruses (GVs). In the occluded forms of baculoviruses, the virions (enveloped nucleocapsids) are embedded in a crystalline protein matrix. This structure, referred to as an occlusion body, is the form found extraorganismally in nature, and it is generally responsible for spreading the infection between insects. The characteristic feature of the NPVs is that many virions are embedded in each occlusion body, which is relatively large (up to 5 micrometers). Occlusion bodies of single nucleopolyhedrosis viruses (SNPVs) are smaller and contain a single virion with multiple nucleocapsids each. Multiple nucleopolyedrosis viruses (MNPVs) have multiple nucleocapsids per virion and multiple virions per occlusion body. Granulosis viruses (GVs) have a single virion with one nucleocapsid per occlusion body. In nature, infection is initiated when an insect ingests food contaminated with baculovirus particles, typically in the form of occlusion bodies. The occlusion bodies dissociate under the alkaline conditions of the insect midgut, releasing the virions, which then invade epithelial cells lining the gut. Within a host cell, the baculovirus migrates to the nucleus where replication takes place. Initially, specific viral proteins are produced within the infected cell via the transcription and translation of so-called “early genes.” Among other functions, these proteins are required for the replication of the viral DNA, which begins 4 to 6 hours after virus enters the cell. Viral DNA replication proceeds up to about 24 hours post-infection (pi). From about 8 to 24 hours pi, infected cells express “late genes” at high levels. These include components of the nucleocapsid that surround the viral DNA during the formation of progeny virus particles. Production of progeny virus particles begins around 12 hours pi. Initially, progeny viruses migrate to the cell membrane where they acquire an envelope as they bud out from the surface of the cell and are then called budding viruses. The non-occluded, budding viruses can then infect other cells within the insect. Polyhedrin synthesis begins approximately 18 hours after infection and increases to very high levels by 24 to 48 hours pi. At about 24 hrs pi, there is a decrease in the rate of non-occluded viruses production, and most progeny virus particles are then embedded in occlusion bodies. Occlusion body formation continues until the cell dies or lyses. Some baculoviruses infect virtually every tissue in the host insect so that at the end of the infection process, the entire insect is liquified, releasing extremely large numbers of occlusion bodies which can then spread the infection to other insects.
One problem associated with the natural insect virus as insecticide is that the virus tends to degrade over time; or upon being exposed to the nature environment (e.g., sunlight) and thereby loses its capability in infecting insect pests. In view of the forgoing reason, there exists in this art a need for developing an improved insect virus that may withstand UV or sunlight; and a method for prolonging the infectious ability of an insect virus.